During the operation of various electrical equipment or installation/restoration procedure, such as transmission line switch operation, switchgear operation or string dropped conductor, a zone of protection against electrical shock is required to protect electrical workers and operators. In general, a permanent or portable gradient control protective device is needed to provide equal potential zone which mitigates touch potential hazard during the work.
Prior art protective devices cannot effectively protect an electrical worker or operator from transmission line level fault current while allowing the electrical worker or operator successfully completes his/her task. Some prior art protective devices have low limit of withstand fault current level which can only be used on the residential or industrial fault level. The actual fault current withstand level of some prior art protective devices is also questionable after the insulation layer becomes deteriorated or worn out. Also, some prior art protective devices are difficult to be inspected before use since the conductive component is hidden inside of the device.
Examples of prior art protective devices are disclosed in the following U.S. Pat. No. 4,637,575 to Yenzer; U.S. Pat. No. 4,885,659 to Nowell et al; U.S. Pat. No. 5,118,578 to Berger et al; U.S. Pat. No. 5,491,892 to Fritz et al; U.S. Pat. No. 5,646,370 to Perkins; U.S. Pat. No. 5,835,332 to White et al and U.S. Pat. No. 6,477,027 to McKelvy.